OTO (Orthotolidine) Test
OTO is a solution that turns yellow when added to chlorinated water. The darker it turns, the more chlorine is present in the water. If the chlorine level is excessively high, then the solution will turn brown. One benefit of an OTO test is that it does not bleach out in the presence of high levels of chlorine.
We did a test where a vial is filled to a level with tap water. Four drops of the OTO solution is added and the water in vial turns yellow. Some uncooked raw rice is added into the yellow solution and is stirred for a few seconds. Then the yellow solution becomes clear again, it was no longer yellow. This shows that the chlorine is being absorbed by the rice. It is therefore better to use filtered water in preparation of food. (I lost the pictures we have taken though)